333 research outputs found
Spin-filtered and Spatially Distinguishable Crossed Andreev Reflection in a Silicene-Superconductor Junction
We theoretically investigate the quantum transports in a junction between a
superconductor and a silicene nanoribbon, under the effect of a magnetic
exchange field. We find that for a narrow nanoribbon of silicene, remarkable
crossed Andreev reflection (with a fraction ) can be induced in the
energy window of the elastic cotunneling, by destroying some symmetries of the
system. Since the energy responses of electrons to the exchange field are
opposite for opposite spins, these transport channels can be well spin
polarized. Moreover, due to the helicity conservation of the topological edge
states, these three transport channels are spatially separated in three
different locations of the device, making them experimentally distinguishable.
This crossed Andreev reflection is a nonlocal quantum interference between
opposite edges through evanescent modes. If two superconducting leads with
different phases are connected to two edges of the silicene nanoribbon, the
crossed Andreev reflection can present Josephson type oscillations, with a
maximal fraction .Comment: 8 pages, 7 figure
Investigating in-service teachers' STEM literacy: the role of subject background and gender
Background:Â STEM literacy has increasingly become a significant educational goal worldwide. Teachersâ STEM literacy is of utmost importance in mediating studentsâ learning. Although many teacher preparation programs are being structured to accommodate the changing educational landscape there is still limited understanding of how teachers engage with STEM.
Purpose:Â The purpose of this paper was to provide a comprehensive framework for tracing teachersâ STEM literacy which can be adapted for empirical investigations. The paper provided both a theoretical framework which consists of STEM knowledge, ability and attitudes and a methodological approach for tracing teachersâ STEM literacy.
Sample:Â This study was conducted with 97 compulsory education teachers (48% female) in China. Overall, 66.0% of the participants taught science in primary and secondary school, 16% taught technology and 17% taught mathematics.
Design and methods:Â The study was guided by two research questions: (a) What were the relationships between the elements of in-service teachersâ STEM literacy? (b) What differences, if any, were there in in-service teacherâ STEM literacy in terms of their subject background and gender? A pilot study confirmed the validation and reliability of the research tool. A series of t-tests and analyses of variance were performed to identify the status quo and any significant differences in teachersâ STEM literacy. Pearson Correlation analysis was conducted to measure the strength of the relationships between each two variables.
Conclusions: The results suggested that the Teachersâ STEM Literacy Survey was valid and reliable for examining teachersâ STEM literacy and indicated (a) teachers performed well in the discipline knowledge (especially in scientific knowledge), but problem-solving ability (PSA) and STEM career interest (CI) were limited; (b) gender differences existed in teachersâ self-efficacy to PSA. Mathematics teachers had relatively lower confidence in PSA and (c) CI might have no correlation with teachersâ understanding of STEM knowledge and STEM ability
Fault-Tolerant Control for Systems with Unmatched Actuator Faults and Disturbances
A fault-tolerant control (FTC) scheme for a class of nonlinear systems with unmatched actuator redundancy and unmatched disturbances is proposed in this note. A methodology to construct unified smooth sliding mode control laws and update laws is proposed such that the equivalent injections of the first-order time derivatives of the unmatched actuator faults and unmatched disturbances can appear in the unmatched channels. The unmatched actuator faults and unmatched disturbances are completely canceled by these equivalent injections. Based on this methodology and using the backstepping design procedure, a set of smooth FTC sliding surfaces, FTC laws and update laws are then designed. With the help of the FTC law selecting mechanism, the output tracking errors of the closed-loop FTC system converge to zero asymptotically, and time-varying faults and disturbances are reconstructed. A simulation example is presented to illustrate the effectiveness of the proposed FTC method
Toward the Tradeoffs between Privacy, Fairness and Utility in Federated Learning
Federated Learning (FL) is a novel privacy-protection distributed machine
learning paradigm that guarantees user privacy and prevents the risk of data
leakage due to the advantage of the client's local training. Researchers have
struggled to design fair FL systems that ensure fairness of results. However,
the interplay between fairness and privacy has been less studied. Increasing
the fairness of FL systems can have an impact on user privacy, while an
increase in user privacy can affect fairness. In this work, on the client side,
we use fairness metrics, such as Demographic Parity (DemP), Equalized Odds
(EOs), and Disparate Impact (DI), to construct the local fair model. To protect
the privacy of the client model, we propose a privacy-protection fairness FL
method. The results show that the accuracy of the fair model with privacy
increases because privacy breaks the constraints of the fairness metrics. In
our experiments, we conclude the relationship between privacy, fairness and
utility, and there is a tradeoff between these.Comment: 17 pages, 3 figures, conferenc
Threshold dynamics of a nonlocal diffusion West Nile virus model with spatial heterogeneity
In this study, we investigated the threshold dynamics of a spatially heterogeneous nonlocal diffusion West Nile virus model. By employing semigroup theory and continuous Fréchet-differentiable, we established the well-posedness of the solution. The expression for the basic reproduction number derived using the next-generation matrix method. The authors demonstrated the threshold dynamics of the system by constructing a Lyapunov function and applying the comparison principle. Finally, numerical simulations were used to validate the theorem results. It can be suggested that to control disease development rapidly, measures should be taken to reduce the spread of mosquitoes and birds
Direct Manipulation of quantum entanglement from the non-Hermitian nature of light-matter interaction
Biphoton process is an essential benchmark for quantum information science
and technologies, while great efforts have been made to improve the coherence
of the system for better quantum correlations. Nevertheless, we find that the
non-Hermitian features induced by the atomic quantum interference could be well
employed for the direct control of entanglement. We report the demonstration of
exceptional point (EP) in biphotons by measuring the light-atom interaction as
a natural non-Hermitian system, in which the electromagnetically induced
transparency regime provides a powerful mechanism to precisely tune the
non-Hermitian coupling strength. Such biphoton correlation is tuned within an
unprecedented large range from Rabi oscillation to
antibunching-exponential-decay, also indicating high-dimensional entanglement
within the strong and weak light-matter coupling regimes. The EP at the
transition point between the two regimes is clearly observed with the biphoton
quantum correlation measurements, exhibiting a single exponential decay and
manifesting the coalesced single eigenstate. Our results provide a unique
method to realize the controllability of natural non-Hermitian processes
without the assistance of artificial photonic structures, and paves the way for
quantum control by manipulating the non-Hermitian features of the light-matter
interaction
Design of FPGA-Implemented Reed-Solomon Erasure Code (RS-EC) Decoders With Fault Detection and Location on User Memory
ReedâSolomon erasure codes (RS-ECs) are widely used in packet communication and storage systems to recover erasures. When the RS-EC decoder is implemented on a field-programmable gate array (FPGA) in a space platform, it will suffer single-event upsets (SEUs) that can cause failures. In this article, the reliability of an RS-EC decoder implemented on an FPGA when there are errors in the user memory is first studied. Then, a fault detection and location scheme is proposed based on partial reencoding for the faults in the user memory of the RS-EC decoder. Furthermore, check bits are added in the generator matrix to improve the fault location performance. The theoretical analysis shows that the scheme could detect most faults with small missing and false detection probability. Experimental results on a case study show that more than 90% of the faults on user memory could be tolerated by the decoder, and all the other faults can be detected by the fault detection scheme when the number of erasures is smaller than the correction capability of the code. Although false alarms exist (with probability smaller than 4%), they can be used to avoid fault accumulation. Finally, the fault location scheme could accurately locate all the faults. The theoretical estimates are very close to the experiment results, which verifies the correctness of the analysis done.This work was supported in part by the National Natural Science Foundation of China under Grant 61501321, in part by the China Postdoctoral Science Foundation and Luoyang Newvid Technology Company, Ltd., and in part by the ACHILLES Project PID2019-104207RB-I00 funded by the Spanish Ministry of Science and Innovation
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